The present disclosure relates generally to earth-boring drill bits for drilling a borehole for the ultimate recovery of oil, gas, or minerals. More particularly, the present disclosure relates to fixed cutter bits including a modular blank assembly and methods for manufacturing fixed cutter bits with a modular blank assembly.
An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. The borehole thus created will have a diameter generally equal to the diameter or “gage” of the drill bit.
Fixed cutter bits, also known as rotary drag bits, are one type of drill bit commonly used to drill wellbores. Fixed cutter bit designs include a plurality of blades angularly spaced about the bit face. The blades generally project radially outward along the bit body and form flow channels there between. In addition, cutter elements are often grouped and mounted on several blades. The configuration or layout of the cutter elements on the blades may vary widely, depending on a number of factors. One of these factors is the formation itself, as different cutter element layouts engage and cut the various strata with differing results and effectiveness.
The cutter elements disposed on the several blades of a fixed cutter bit are typically formed of extremely hard materials and include a layer of polycrystalline diamond (“PD”) material. In the typical fixed cutter bit, each cutter element or assembly comprises an elongate and generally cylindrical support member which is received and secured in a pocket formed in the surface of one of the several blades. In addition, each cutter element typically has a hard cutting layer of polycrystalline diamond or other superabrasive material such as cubic boron nitride, thermally stable diamond, polycrystalline cubic boron nitride, or ultrahard tungsten carbide (meaning a tungsten carbide material having a wear-resistance that is greater than the wear-resistance of the material forming the substrate) as well as mixtures or combinations of these materials. The cutting layer is exposed on one end of its support member, which is typically formed of tungsten carbide.
While the bit is rotated, drilling fluid is pumped through the drill string and directed out of the face of the drill bit. The fixed cutter bit typically includes nozzles or fixed ports spaced about the bit face that serve to inject drilling fluid into the flow passageways between the several blades. The flowing fluid performs several important functions. The fluid removes formation cuttings from the bit's cutting structure. Otherwise, accumulation of formation materials on the cutting structure may reduce or prevent the penetration of the cutting structure into the formation. In addition, the fluid removes cut formation materials from the bottom of the hole. Failure to remove formation materials from the bottom of the hole may result in subsequent passes by cutting structure to re-cut the same materials, thereby reducing the effective cutting rate and potentially increasing wear on the cutting surfaces. The drilling fluid and cuttings removed from the bit face and from the bottom of the hole are forced from the bottom of the borehole to the surface through the annulus that exists between the drill string and the borehole sidewall. Further, the fluid removes heat, caused by contact with the formation, from the cutter elements in order to prolong cutter element life. Thus, the number and placement of drilling fluid nozzles, and the resulting flow of drilling fluid, may significantly impact the performance of the drill bit.
Fixed cutter bits are conventionally either machined from steel or made of a hard metal cast matrix formed in a mold with a bit blank disposed in the mold. For matrix bits, the mold must be created or machined and the bit blank is made from steel or other suitable material is prepared and disposed within the mold cavity. The bit blank provides reinforcement to the bit body matrix and accommodates spacers (e.g., sand castings) that define drilling fluid passages through the bit body. In general, the spacers are positioned in the mold (along with the bit blank) during formation of the bit body, and the spacers are removed after formation of the bit body to leave drilling fluid passages in the bit body. The bit blanks are individually custom designed and created, and often need to be completely remade when minor changes to the drill bit design are made. Further, the bit blank must be precisely positioned within the mold to ensure the proper placement of the spacers for drilling fluid passages.
A quantity of particulate material is then introduced to the mold to form the bit body matrix. The bit body is then either heated or molten metal is introduced to the particulate material, forming a solid bit body. The bit body may then be attached or secured to other drill bit components through welding, and cutting elements may be secured to the bit body by brazing, adhesive bonding, or other mechanical means. Thus, the process of manufacturing a particulate-based drill bit is complex, lengthy, time intensive, and costly. Furthermore, the associated thermal impact of the manufacturing processes can cause thermal stress and cracking to develop in the bit body. When the bit body is being heated, the steel of the blank tries to expand while the matrix material does not, which puts tensile stress around the matrix and creates hoop stress. When the bit body begins to cool down after welding or brazing, the blank tries to shrink, but the matrix material restrains it putting further pressure on the interior matrix.